Is it just me, or does the audio sound like like she's saying "interessante"? I'd love to hear the difference in sound here. Because the way it is pronounced here sounds exactly like the word "interesante" in Spanish, so it confuses my poor brain >:(

Yes, you're right! If you use the definite article, then you always have the -e form, e.g. de interessante vrouw, het interessante meisje. But if you use the indefinite article, then you only use the -e form with the de-words, e.g. een interessante vrouw, een interessant meisje